The present invention relates to a method and a device for forming locally compressed regions on absorbent products.
Absorbent products, in particular female hygiene products, e.g. panty liners, sanitary napkins, etc. and diapers and incontinence protection products, are usually provided with fold lines which help control the shape that the product takes up during use. These fold lines can be produced by selectively compressing some or all of the material comprised in the absorbent product in order to form lines of locally compressed material. These lines of compressed material can, for example in a panty liner, be placed in the longitudinal direction and given an anatomically adapted shape. During use the panty liner is easily deformed into a bowl-like shape which more closely conforms to the anatomy of the user and thereby is more comfortable to wear and provides greater security against leakage. Local compressions can also act as trenches which prevent or reduces the spread of fluid laterally, thereby reducing leakage. In certain materials the compressed material in the compression lines has an increased capillary action which helps distribute the fluid better in the longitudinal direction.
Compression lines can be formed on the finished product or can be formed only on a constituent part, e.g. an absorbent body, before it is incorporated into a product.
It is often difficult to produce permanent compression lines in absorbent products, especially if they comprise absorbent bodies made of resilient material such as e.g. chemithermomechanical pulp (CTMP), chemical pulp, polymers or the like. These resilient fibres tend to return to their uncompressed shape after having been compressed and the compression lines become impermanent. One way of making the effects of the compression more permanent is to increase the moisture content of the item being compressed. This can be achieved by increasing the environmental humidity in the machine where the compressing takes place and/or by directly spraying water or some other fluid onto the material before it is fed into the forming machine. The increased humidity can lead to chemical bonds forming between fibres which are in contact with each other.
EP-A 0 678 608 describes a method for manufacturing an absorbent fibre layer for use in such products, in which a surface of said layer is provided with a pattern of compressed regions. The compressed regions are formed by moistening the lower surface of the fibre layer and compressing it by hot-calendering. The moistening is performed by a water nozzle or a steam box which supplies moisture to substantially the whole of the web.
Raising the moisture content of the material in this way can lead to negative consequences: the material can become sticky and fasten in moulds and onto transfer rollers leading to increased down-time while the machinery is cleaned. This increased stickiness can lead to the material clumping together which means that the risk that hard spots can occur in the product also increases. In addition some of the added moisture can be absorbed by superabsorbent particles or liquids (i.e. products able to absorb many times their own weight of liquid) in the material which naturally reduces their ability to absorb body fluids later.
An object of the present invention is to provide a method which can produce permanent compression lines in a material without the disadvantages of previous know methods.
A further object of the present invention is provide absorbent products with permanent compression lines.
The objects of the present invention are achieved by locally moistening the material in which compression lines are to be formed only in the regions intended to form compression lines. In a method according to the invention this is achieved by providing the compression means which forms the compression lines with openings through which moisture can be provided only to the material intended to be compressed during the compression operation.